Motors are a type of machine that produces rotational power by converting electrical energy into mechanical energy. Motors are generally divided into alternating current (AC) motors and direct current (DC) motors, in which induction motors are a type of AC motors.
Induction motors are a representative type of AC motors in which current is induced to a secondary winding in response to electromagnetic induction of a first winding connected to a power supply. Rotational torque is produced due to interaction between the current induced to the secondary winding and a rotating magnetic field.
Such an induction motor generally includes a stator, a rotor, which is concentric with the stator and maintains a predetermined gap on the inner circumference of the stator, and a shaft, which is pressed into the central portion of the rotor and transfers rotational power of the rotor to a following shaft.
The stator includes a coil, which forms a rotating magnetic field in response to an AC source applied thereto, and a core, which forms a path of a magnetic flux generated by the rotating magnetic field. The stator core is implemented by stacking a plurality of circular electrical steel sheets on one another, each of which has a plurality of radial stator slots on the inner circumference thereof. The coil is wound through a stator slot by a variety of methods.
The rotating magnetic field is generated due to the AC source applied to the coil so that a magnetic flux rotates through the stator coil. The rotating magnetic flux intersects a rotor conductor, thereby inducing current to the rotor conductor. Here, the current induced to the rotor conductor cooperates with the magnetic flux to generate torque due to Fleming's left hand rule.
Such a stator of an induction motor is fabricated by winding a coil, which is a conductive wire, on a core considering its structural characteristic. This is an essential element for rotating the rotor by forming a rotating magnetic field due to alternating current.
However, when the power of the super-high-speed motor is greater or the super-high-speed motor is used for a longer time, the endurance of the super-high-speed motor degrades more due to heating. Therefore, efficient cooling is essential. When more heat is generated, the endurance of the induction motor deteriorates and insulation is subjected to irreversible deterioration.
A variety of cooling methods is applied in order to dissipate heat that is generated by the inductor motor. In an example, a method of cooling the stator due to heat exchange by forcibly introducing a circulation liquid into the stator is used. In addition, for the purpose of effective heat dissipation, cooling efficiency is increased by filling a hollow space present between the core and the coil, which constitute the stator, with a material having excellent insulation and heat conductivity.
When the hollow space between the core and the coil is filled with the heat conductive material, a great number of bubbles are created inside the heat conductive material, between the heat conductive material and the core, and between the heat conductive material and the coil, thereby degrading heat conductivity. This consequently causes the problem of a localized increase in temperature, thereby creating thermal fracture.